This invention is in the field of asphalt compounds; more particularly, the invention relates to a modified roofing asphalt formulation.
Two types of asphalt coated roofing materials are available; built up roofs, and roofs made of roofing shingles. Built up roofing is the type used on horizontal type roof structures which are typically commercial or apartment type buildings. For the built up roofs, asphalt is heated to 400.degree.-450.degree. F., and then mopped on. The saturated asphalt felt is then rolled over. The asphalt which acts both as an adhesive as well as a water-proofing coating, is applied as the roof is being layed down. Because the asphalt for built up roofing must retain adhesive properties, it is less crosslinked or mildly oxidized compared to asphalt prepared for roofing shingles. Roofing stone aggregate is spread over the entire built up roof to provide weather resistance to the built up roof. Roofing stone aggregate cann be stone or slag. Its purpose is to prevent ultraviolet rays from degrading the roof coating. The stone allows walking over the roof without disturbing the asphalt.
Roofing shingles are another type of roofing material coated with asphalt. The asphalt is crosslinked or oxidized and is coated onto the roofing felt in a manufacturing step. Generally, the asphalt is filled with stone dust. The asphalt is heated to about 400.degree.-450.degree. F. and spread on and pressed into the roofing felt. Roofing granules are then fed onto the saturated asphalt felt and pressed in.
Roofing felt from a continuous roll is coated with the asphalt formulation at about 400.degree. F. Roofing granules, a colored ceramic stone baked onto stone granules, are pressed into the coating. The shingle color becomes the color of the granules. This coated felt roll is cooled and the shingles, with desired cut-outs, are continuously cut from the continuous shingle roll. Typically, the roll is three feet wide and shingles are one by three feet with cut-outs.
In recent years roofing felt material has been changed from cellulose to glass fibers. The new glass fiber shingle is thinner and more flexible than the old cellulose felt shingle. Therefore, the coating must have better flexibility properties, particularly at cold temperatures. If this is not the case, flexing at cold temperatures causes surface cracking in the shingles. The cracks are failure sites and points for future leaks to develop.
In addition to the change of material for the asphalt roofing felt, the origin of asphalt supplies have changed in recent years, from domestic crudes to Venezuela, Arabian or North Slope sources. These new changes have made it necessary to re-evaluate the construction and composition of roofing shingles and their components, particularly the asphalt coatings. However, asphalts from various sources are commonly blended for uniformity. There is, therefore, a need, in view of the changing requirements of asphalt roofing shingles, to develop a roofing asphalt formulation which can readily be substituted for existing asphalt shingles, both in processing and application.